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Polk SDA SRS Inspired or just crazy?

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  • Polk SDA SRS Inspired or just crazy?

    I am really interested in building a pair of large towers. My inspiration comes from some really classic and great sounding speakers. If you have ever heard the old classic polk sda srs speakers you know what I am talking about. I don't want to build the huge towers with 8, 6.5" speakers. I was thinking of doing this with 4, 6.5" and two soft dome tweeters which is still pretty big. Then using a either the 15" or a 12" passive radiator. The box would be fairly simple with two tweeters up top and isolated then the four 6.5" and passive radiator at the bottom. I would not be building the stereo dimensional array portion of the crossover at all.

    I don't know though if it really would be a good plan however. I have read a bit about design and it sounds like this is a classic out dated design. My concern is that these would have one sweet spot in the middle of the room and that is it. Does that really matters though as I have a dedicated theater room? Everything now is slim design with usually two at most 6.5 speakers. So my thought is that maybe I should scale back a bit but not sure. I would like to be able to draw a flat line from 20-20hz. I like the speed and clarity of a smaller 6.5 speaker. Also would like to update my other speakers so they have matching 6.5" speakers all around. This way the voice coil in everything would match.

    Another thought would be to stick with a slimmer design and instead of using a active subwoofer on the side use the passive radiator. I would see this cabinet design as looking more like the current Polk ti line. The difference is that I would add more 6.5" drivers so that I could get the bass I want with those and the radiator.

    Any thoughts?

    What I would really like is a pair of 802 B&W's. Could someone just drop those off and a two mono block VTL amps? :D

  • #2
    Re: Polk SDA SRS Inspired or just crazy?

    Sounds like you want to built some SDA 1C. The design is not outdated in so much as it does not have wife appeal. The presense of a large "wide" speaker is not appealing to most but is needed for the classic SDA design to work.

    Comment


    • #3
      Re: Polk SDA SRS Inspired or just crazy?

      As I understand, the polk SDAs were designed to produce controlled dispersion. Getting the dispersion right on speakers like that can be tricky. Also, if Stereophile's measurements are an indication, the 802's polar plots aren't so good - there's a major droop in midrange response if you get too far off-axis.

      A somewhat more modern solution to the problem is to use waveguides, which can give you a ~60-~90 degree sweet spot very nicely. Alternately, large improvements made to small drivers mean you can make a speaker with a really wide sweet spot by either using very small drivers on a narrow baffle or the various not-quite-omnidirectional designs out there. (Look up the SoundRounds for one that proved very cost effective). There are also the various dipole designs, which have very controlled directivity all the way through the bass region in trade for efficiency.

      I'd listen to some speakers and see what you like. It might be that what you're looking for is just a big speaker's ability to produce very loud transients without distorting, something big monsters like the Polks can do very well indeed.

      Comment


      • #4
        Re: Polk SDA SRS Inspired or just crazy?

        So if I understand what you are saying because of the width of the box they have a 30 degree listening position. After that you are pretty much out of any sort of sweet spot. I am sure for the most part I would be in that sweet spot but not a huge fan of the big box either. I think I have something in mind that I would like better.

        I am not a fan of mirage at all from listening standpoint so I would not going with anything omni directional. I am a huge fan of B&W and how transparent they sound but don't have the funds. I realize the bigger B&W's are a three way speaker however some B&W's are a two way design (quite nice sounding as well). What if I was to build something more like a Polk TSi500 with a passive radiator? That way I could stick to a simpler design of having a two way cross over. Then I would get away from port noise with the radiator. I would still have the fast response of smaller drivers and be able to brace the box more easily. I could put the radiator on the side of the box instead of the front. This way they should be able to produce effortless deep sounding bass and very warm mid range.

        Are passive radiators difficult to work with? I find it odd that everything has gone to a ported design yet everyone talks about port noise. Its like saying yeah we know the standard is messed up so here is how we fix it. Everyone has different ways to resolve that issue, B&W use a golf ball design where as other designers have different solutions. A sealed box lends itself to being very large, so why not go with a passive radiator. Seems to solve both solutions. You can build a smaller box and have zero port noise. Also based on the sealed inclosure design you can get a better range. So am I missing something.

        Comment


        • #5
          Re: Polk SDA SRS Inspired or just crazy?

          Hey UtahSaint. I sent you a PM. If you get to the point you need some measurements or something, let me know.

          Comment


          • #6
            Re: Polk SDA SRS Inspired or just crazy?

            I suspect what you like about B&W is low harmonic distortion and a well designed crossover. You'll find these characteristics in quite a few DIY designs that are already tried, tested and proven. There's lots of variables to consider before considering the variations.

            I suggest you consider the room first and speaker placement limitations if any. If you plan on using existing amplification, best to consider the output power and the ability to drive highly resistive loads of 4-5 ohms. Please post some more details and we might be able to better assist you in your quest for an upgrade.

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            • #7
              Re: Polk SDA SRS Inspired or just crazy?

              Are you planning to replicate Polk's SDA effect as well? This is sort of like Dynaquad in that it involves adding a L-R and R-L. In addition to the speaker wires going from the amp to the speakers, the SDAs also had a wire going from one speaker to the other.

              Comment


              • #8
                Re: Polk SDA SRS Inspired or just crazy?

                Does anyone know exactly what the SDA circuit did in that series of Polks? I remember hearing them and they were ok, maybe good. Either way, I do remember the effect was quite audible.

                Comment


                • #9
                  Re: Polk SDA SRS Inspired or just crazy?

                  Originally posted by dwigle View Post
                  Does anyone know exactly what the SDA circuit did in that series of Polks? I remember hearing them and they were ok, maybe good. Either way, I do remember the effect was quite audible.
                  I think it's sort of like #2:



                  pun intended

                  Comment


                  • #10
                    Re: Polk SDA SRS Inspired or just crazy?

                    Somewhere on line there is a diagram, but basically each speaker (LR) has a horizontal array. One driver plays in phase, the other driver plays the opposite channel out of phase. The two drivers are about a heads width apart, so the left ear hears the left channel, the right channel is cancelled. Right ear hears right channel, and cancelled left. So, you end up with a headphones. Try it yourself with those $2 buyouts. Put two each on a baffle about a foot apart, firing straight ahead, no toe in.

                    Comment


                    • #11
                      Re: Polk SDA SRS Inspired or just crazy?

                      I do not plan on replicating the SDA portion of the speakers although there is some interest in that. From what I understand though that would require a box design where two drivers would be side by side. That has a very limited on access sound and as someone else stated which only gives you 30 degrees of great sound. Also this is for a 5.1 or 7.1 theater. The design of SDA was never meant for theater but only stereo music as I understand it. With a center channel that really would mess with the sound. Although it made for some amazing stereo sound.

                      To answer some questions:

                      I have a dedicated theater room with the following dimensions:

                      12 1/2 feet wide
                      7 1/2 feet tall (might end up taller by removing the drop ceiling and putting in dry wall. I hate it when the ceiling vibrates.)
                      32 feet in length. Seats are at 12 feet back and can be moved if needed.

                      My current system is as follows:
                      96' movie screen with a 1080p projector.
                      Infinity Crescendo 3006 speakers with replaced Peerless classic 8' subs
                      (one blew out again and suspect something is bad in the cross over)
                      Pioneer elite thx receiver which is able to bi amp the front, 130 watt per channel (thinking of maybe going to separates or at least a high power stereo amp for the front channel. I love all types of music as well.)
                      I have a Polk Audio sub woofer, center and klipsch surround for now and a blue ray player. In all the system sounds pretty amazing but I keep running into issues with blown drivers every so often. Also the speakers do not quite have the imaging and low harmonic distortion that I am looking for.

                      Comment


                      • #12
                        Re: Polk SDA SRS Inspired or just crazy?

                        Here is what I am looking at so far for speakers.

                        Tang Band 25-1372SC 1" Titanium Tweeter.
                        These have an amazing flat response my only concern would be do they sound tingy? I have heard some not so great things about metal tweeters. Also they seem to have a peek at 20 hz but will run to 30 Hz.

                        The HiVi RT2C Planar Isodynamic Tweeter sounds very interesting. It has a very flat response as well. Not sure what people think of those. I find the Martin Logan treble as well as mid range to be some of the best sounding on the market. These are different but compared to the same sound. They break up in some sound listening cases but they can produce some amazing sound as well. I once heard rain on Martin Logan's and couldn't believe it. Then we walked away when U2 was playing on them. They just didn't hold together well at all in mid to bass. Also my concern is off axis sound.

                        Drivers:

                        Tang Band (once again) W6-789e 6-1/2 woofer.
                        Very flat graph the specifications don't look great but the graph looks amazing. These speakers don't really have many peaks. I kind of worry that they won't take much power but 4 of these are going in each box. So that would 120 maximum power and whatever the tweeter can handle. These are 92 db sensitivity so they would go with the tweeter choices very well. Also if the receiver is set to 7.1 and not bi amp it wouldn't be an issue.

                        12" Passive Radiator
                        Dayton Audio SD315-PR 12" Passive Radiator. This is rated to go down to 17 Hz.

                        Over all that would put these at 17 Hz - 30,000 Hz so goal 1 would be achieved at somewhere around 92 + db sensitivity. The next step would be to build a cross over to keep them flat. I am not sure what a radiator does to the bass curve but I can image it can really create too much.

                        The box dimensions from WinISD pro came out with 3.75 cu. ft. with the radiator.

                        Comment


                        • #13
                          Re: Polk SDA SRS Inspired or just crazy?

                          So I have had a lot of help from other members (thanks a ton). What we came up with is a few things. Polks had an amazing frequency response and maybe not so great of a mid. They also had a very limited on off axis sound quality. Lining up a bunch of 6.5 speakers would give me a very good mid to treble range but there would be nothing past the 45 hz range. Not even a passive radiator will pick up enough to make it much beyond that. The mids would burn up trying to produce too much sound. Also the box would be completely unsightly huge. Not to mention the cost, putting all this together without the cross over and mdf was already over $800. So onward and upward. I am however sold on the tang bang speakers at least in theory. So to start I am going to build a pair of monitors. That is where everyone says to start. My decision will be to port them tuned to 45 or 50 hz as well. That should give me a very decent sounding book shelf speaker. Actually it should be better sounding than my older Infinity Crescendos. I don't think it would have the impact but it should produce some very clean and beautiful sound.

                          So now to design a ported book shelf speaker, and cross over based on the 6.5 tang band W6-789E and the Tang Band 25-1372SC tweeter.

                          Comment


                          • #14
                            Re: Polk SDA SRS Inspired or just crazy?

                            Originally posted by utahsaint View Post
                            So I have had a lot of help from other members (thanks a ton). What we came up with is a few things. Polks had an amazing frequency response and maybe not so great of a mid. They also had a very limited on off axis sound quality. Lining up a bunch of 6.5 speakers would give me a very good mid to treble range but there would be nothing past the 45 hz range. Not even a passive radiator will pick up enough to make it much beyond that. The mids would burn up trying to produce too much sound. Also the box would be completely unsightly huge. Not to mention the cost, putting all this together without the cross over and mdf was already over $800. So onward and upward. I am however sold on the tang bang speakers at least in theory. So to start I am going to build a pair of monitors. That is where everyone says to start. My decision will be to port them tuned to 45 or 50 hz as well. That should give me a very decent sounding book shelf speaker. Actually it should be better sounding than my older Infinity Crescendos. I don't think it would have the impact but it should produce some very clean and beautiful sound.

                            So now to design a ported book shelf speaker, and cross over based on the 6.5 tang band W6-789E and the Tang Band 25-1372SC tweeter.
                            To be brutally honest, reading this thread, it is obvious that you are very much lacking in the necessary knowledge to properly design a speaker, ported or otherwise. There is a substantial learning process involved. If you need an uncommon design, necessitated by unique requirements, there may not be an existing design available meeting those requirements, forcing you to come up with your own. However since you have now decided that a monitor will do and so many designs for these are available, you should be able to find an existing one which fulfills your requirements. As is stated before in many threads, start with an existing design and build from there.

                            If you still decide to design your own, there are 2 possible outcomes: You do it all yourself and the outcome will be mediocre at best or you will tap the brains of some of the many talented individuals on this forum for all aspects of the design and you end up with something that sounds good. However it won't be your design!

                            .
                            Don't worry, if your parachute fails, you have the rest of your life to fix it.

                            If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

                            Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

                            Comment


                            • #15
                              Re: Polk SDA SRS Inspired or just crazy?

                              Its okay I am here to learn. It was more an exercise for me to understand modern speaker design. Also if it is possible to build something better than the classic polk sda in a more modern vertical design. In other words creating something with a much better sweet spot. Another way to look at this might be that they don't make mid range drivers anything like what it would take. Also that modern design is all about porting, slots or some other method to make the speaker boxes smaller. So in reality the market has determined what products and methods are available. It seems if you want something with a straight frequency response it will take a different design approach. Most likely a three way design that is ported. This is not a bad thing but a fork in the road none the less. I don't see it as not understanding design but understand what is available. Obviously passive radiators and large boxes were very much a part of speaker design at one time. Also this is my end goal not a starting point. I understand I have to start somewhere.

                              I have a feeling I could create a very good two way monitor speaker. Yes it would take a lot of time, some failures here and there. Also it would require help from others. I don't see that as a bad thing. I could just buy a box from Parts Express that is pre built and be done. However I don't feel that you learn a thing from that process. I would rather fail miserably a few times and get something right than buy pre built and not understand a thing. So the cross over network will have to be easily accessible and I will have to lean the proper way to build a box.

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